//给定一个二叉树，找出其最大深度。 
//
// 二叉树的深度为根节点到最远叶子节点的最长路径上的节点数。 
//
// 说明: 叶子节点是指没有子节点的节点。 
//
// 示例： 
//给定二叉树 [3,9,20,null,null,15,7]， 
//
//     3
//   / \
//  9  20
//    /  \
//   15   7 
//
// 返回它的最大深度 3 。 
// Related Topics 树 深度优先搜索 广度优先搜索 二叉树 👍 1081 👎 0

package leetcode.editor.cn;

import java.util.LinkedList;
import java.util.Queue;

public class MaximumDepthOfBinaryTree{
    public static void main(String[] args) {
//        Solution solution = new MaximumDepthOfBinaryTree().new Solution();
        TreeNode root = new TreeNode(3);
        root.left = new TreeNode(9);
        root.right = new TreeNode(20);
        root.right.left = new TreeNode(15);
        root.right.right = new TreeNode(7);
        System.out.println(new MaximumDepthOfBinaryTree().new Solution().maxDepth(root));

    }
//leetcode submit region begin(Prohibit modification and deletion)

public static class TreeNode {
    int val;
    TreeNode left;
    TreeNode right;
    TreeNode() {}
    TreeNode(int val) { this.val = val; }
    TreeNode(int val, TreeNode left, TreeNode right) {
      this.val = val;
      this.left = left;
      this.right = right;
    }
}

class Solution {
    public int maxDepth(TreeNode root) {
        if (root == null) return 0;
        /*        dfs
        int maxDepthOfLeft = maxDepth(root.left);
        int maxDepthOfRight = maxDepth(root.right);
        return Math.max(maxDepthOfLeft, maxDepthOfRight) + 1;
        */
        Queue<TreeNode> queue = new LinkedList<>();
        int layer = 0;
        queue.offer(root);
        while (!queue.isEmpty()) {
            Queue<TreeNode> tmp = new LinkedList<>();
            for (TreeNode cur : queue) {
                if (cur.left != null) tmp.offer(cur.left);
                if (cur.right != null) tmp.offer(cur.right);
            }
            queue = tmp;
            layer++;
        }
        return layer;
    }
}
//leetcode submit region end(Prohibit modification and deletion)

}